There is demand for pixel miniaturization and pixel sensitivity improvement in photoelectric conversion apparatuses such as CMOS sensors.
With the solid-state imaging apparatus disclosed in Japanese Patent Laid Open No. 2004-193547, a P-type separating layer and a P-type well layer are disposed between an N-type epitaxial layer and an N-type floating diffusion region (FD) in a photodiode. A P-type separating layer and a P-type well layer are also disposed between the N-type epitaxial layer of the photodiode and the N-type epitaxial layer of a photodiode of an adjacent pixel. Therefore, according to Japanese Patent Laid Open No. 2004-193547, electrons produced by the photodiode are stored in the N-type epitaxial layer with certainty due to the various potential barriers surrounding the N-type epitaxial layer, which is described as improving the pixel sensitivity.
Japanese Patent Laid-Open No. 2004-193547 discloses forming a P-type separating layer and a P-type well layer respectively by implanting boron ions in an N-type silicon substrate. As a specific example of the conditions of this process, the P-type separating layer is formed by implanting the substrate with a dose amount of 6×1011/cm2 of boron ions at an energy of 1200 KeV. The P-type well layer, meanwhile, is formed by implanting the substrate with a dose amount of 1012/cm2 of boron ions at an energy of 500 KeV.
The boron tends to diffuse if heat treatment is carried out after the formation of the P-type separating layer and P-type well layer, and thus there is the possibility that the volume of the N-type epitaxial region, which serves as the cathode of the photodiode, will drop. This reduces the magnitude of the charge that can be stored in the N-type epitaxial region of the photodiode, resulting in the possibility that a drop in the sensitivity of the photodiode will appear in the pixel. In other words, there is the possibility that, if the distance between adjacent photodiodes (photoelectric converting units) decreases, the sensitivities of the photodiodes (photoelectric converting units) will drop.